1. Field of the Invention
The invention relates to piezoelectric devices and, more specifically, piezoelectric motors, being electric motors using piezo crystals for providing rotational momentum to a rotor part of the motor relative a stator part of the motor.
2. Description of the Prior Art
A piezoelectric motor is known from U.S. Pat. No. 4,453,103, granted Jun. 5, 1984, comprising a stator and a rotor, which are in mechanical contact with one another along at least one cylindrical surface of friction interaction. Elastically curved, longitudinally elongated plates/pushers, which are set against the friction surface at one end, and are positioned at an angle to the same surface, while being anchored at the other end, either directly or via a metal membrane, to the cylindrical surface of the ring piezoelectric element with electrodes for exciting longitudinal oscillations of the perpendicular surfaces of friction interaction.
U.S. Pat. No. 4,959,580, issued Sep. 25, 1990 describes a piezoelectric motor, possessing the same attributes, except that the pushers are at one end anchored on the flat surface of the ring piezoelectric element.
The maximum power which can be supplied to the piezoelectric element of the above motors is determined by the maximum braking strength of the piezoelectric element or the strength of the bond between the electrodes of the piezoelectric element coating and the ceramics, when the pushers are anchored on the piezoelectric element""s surface. A small diameter of the piezoelectric element will not allow a large number of pushers to be anchored in order to increase the motor""s torque moment. Solving the above problems requires increasing the diameter of the piezoelectric element and, consequently, the piezoelectric element""s volume, which significantly increases the motor""s size and cost. The presence of recesses in the piezoelectric element and the thermal shocks that the piezoelectric ceramics is subjected to when the pushers"" connections are being soldered on it, notably reduces the motor""s reliability, especially in the modes of operation approaching the limit of tolerance. Moreover, such is the technology of anchoring pushers that it requires sizable expenditures when each new type of motor is introduced to the manufacturing process.
It is an object of the invention to provide piezoelectric motors of improved reliability.
It is a further object to provide piezoelectric motors which can be readily disassembled and repaired.
The aforesaid objects are achieved in a general sense by use of retainer means which embrace the piezoelectric element and presses one end of the pusher in satisfactory acoustic contact with the piezoelectric element. The retainer is releasable when desired to free the pusher plates for replacement and the like.
Accordingly, in one aspect the invention provides a piezoelectric motor comprising:
a stator;
a rotor having a rotor inner circumferential surface;
a piezoelectric element retained on said stator;
power supply means in communication with said piezoelectric element to operably effect longitudinal resilient mechanical oscillations in said element;
a plurality of pusher members each having (a) at least one first portion defining a pusher abutting surface abutting said rotor inner surface, (b) at least one second portion defining a piezoelectric element engaging surface distal of said pusher abutting surface, and (c) a third portion defining a retained surface;
retainer means in abutment with said pusher member retained surface to releasably retain said pusher member in abutment with said piezoelectric element engaging surface and said rotor inner surface and wherein said longitudinal resilient mechanical oscillations effect coplanar movement of said pusher member;
and said first portion is so shaped and inclined as to operably effect circumferential movement of said rotor circumferential surface when said pusher member conducts longitudinal resilient mechanical movements induced by said piezoelectric effect element to effect rotary movement of said rotor inner circumferential surface relative to said piezoelectric element.
Preferably, the retainer means comprises (a) a ring member having a diameter and a circumferential inner surface having at least one portion engageable with a said support surface of said third portion of said pusher member to retain said pusher member in suitable engagement with said piezoelectric element and said rotor circumferential surface, and (b) ring diameter adjusting means connectable to said ring to enable said ring diameter to be changed.
Most preferably, each of the pusher members is a curved, longitudinally elongated member formed of a plastics material.